Manufacture of 3-methyl-tetrahydrofuran from 2-methyl-gamma-butyrolactone

ABSTRACT

Disclosed is a hydrogenation process for the preparation of 3-methyl-tetrahydrofuran from 2-methyl-gamma-butyrolactone. The above process enables the production of the objective highly pure 3-methyl-tetrahydrofuran free from alcohol in high efficiency and high conversion through a simple production step.

FIELD OF INVENTION

[0001] Described is a process, for preparing 3-methyl-tetrahydrofuranfrom 2-methyl-gamma-butyrolactone.

BACKGROUND OF THE INVENTION

[0002] Substituted tetrahydrofuran, like 3-methyl-tetrahydrofuran of thepresent invention, is in general useful in those areas in whichtetrahydrofuran is useful. Examples include polymerization to obtainfibers, and uses as a solvent.

[0003] Poly (tetra methylene ether glycol) is obtained by polymerizationof tetrahydrofuran. This polymer is used as chain segments inpolyurethanes and polyesters. Polyurethanes based on poly (tetramethylene ether glycol) soft-segment have improved hydrolytic stability,abrasion resistance and elastomeric properties. Other benefits includestrength, toughness, durability, low compression set property, and highwater vapor permeability. The largest end-use area is in spandex fibersfor apparel. The products containing poly (tetra methylene ether glycol)are used in wheels, high-speed rolls, automotive parts, bushings,specialty hose, cable sheathing and coating, pipeline liners, roof, andfloor coatings. The 3-methyl-tetrahydrofuran monomer can be utilized asa comonomer for modifying poly(tetra methylene ether glycol) to yieldbetter elastomeric properties.

[0004] In use of tetrahydrofuran as a solvent where lower volatility isdesired, 3-methyl-tetrahydrofuran is advantageous becausetetrahydrofuran boils at 66° C. whereas 3-methyl-tetrahydrofuran boilsat 86° C.

[0005] The present invention describes a process to prepare3-methyltetrahydrofuran from 2-methyl-γ-butyrolactone with novelcatalyst systems, without any alcohol production or separation. By“2-methyl-gamma-butyrolactone” is meant the compound described by theformula below.

[0006] Processes for producing 3-methyl-tetrahydrofuran by hydrogenationof an itaconic acid ester or a 3-formyl-2-methylpropionic acid ester,and by hydrogenation of a methyl-succinic ester are described inJapanese Patent Applications 219981/1994 and 217768/1996, respectively.Along with the objective 3-methyl-tetrahydrofuran, these reactionsproduce an alcohol, which has to be separated in a further step. The3-methyl-tetrahydrofuran forms an azeotropic mixture with most of thelower alcohols, for example, with methanol having an azeotropic point at64.5° C., and an azeotropic composition consisting of 25% by weight of3-methyl-tetrahydrofuran and 75% by weight of methanol. The existence ofthis azeotrope necessitates a costly, energy intensive separation stepto yield pure 3-methyl-tetrahydrofuran. In particular, the3-methyl-tetrahydrofuran that is employed for modifyingpoly(tetramethylene glycol) can tolerate an alcohol impurity of notgreater than 0.2%.

[0007] Similarly, U.S. Pat. No. 5,990,324 describes a three-step processfor producing 3-methyl-tetrahydrofuran by hydrogenation ofbeta-formylisobutyric acid ester with the following general formulaROOC—CH(CH₃)—CH₂—CHO wherein, R is an alkyl group having 1 to 3 carbonatoms and the formyl group may be present as an acetal having an alkanolwith 1 to 8 carbon atoms. In this process, the alcohol byproduct isseparated from 2-methyl-gamma-butyrolactone in the second step. Thisseparation can be effected by simple distillation. Although azeotropicdistillation is not required, a separation of the alcohol is still anecessary step in the process of producing 3-methyl-tetrahydrofuran.

[0008] Thus, the problem to be solved is to provide a simple,economical, one-step process for the production of3-methyl-tetrahydrofuran. The one-step process of the present inventiondescribes a more efficient route a to produce 3-methyl-tetrahydrofuranfrom 2-methyl-gamma-butyrolactone with novel catalyst systems, withoutany alcohol production and therefore eliminating the step of azeotropicor other type of separation.

SUMMARY OF INVENTION

[0009] This invention relates to a process for producing3-methyl-tetrahydrofuran (II), by hydrogenating2-methyl-gamma-butyrolactone (I).

DETAILED DESCRIPTION OF THE INVENTION

[0010] This invention relates to synthesis of 3-methyl-tetrahydrofuranfrom 2-methyl-gamma-butyrolactone reactant. More specifically, thisinvention relates to synthesis of 3-methyl-tetrahydrofuran from2-methyl-gamma-butyrolactone, which is free from an alcohol as a sideproduct. The final product does not need separation or purification ofalcohol. Unconverted 2-methyl-gamma-butyrolactone can be isolated andrecycled to the hydrogenation reactor to increase the overall yield ofthe 3-methyl-tetrahydrofuran, the final product. Since2-methyl-gamma-butyrolactone is a higher boiling substance, it can becondensed back to supplement the feed.

[0011] In the process herein, 2-methyl-gamma-butyrolactone is heated attemperatures set forth below, in the presence of hydrogen and thusreduced by hydrogenation to yield 3-methyl-tetrahydrofuran, the desiredproduct. A metal catalyst, with or without a support may be present toeffect the reduction reaction. An acid system may be used as a promoterto effect the reaction. A metal may also be optionally used as apromoter to aid the reaction.

[0012] The process of the present invention may be carried out in batch,or continuous mode in any of the equipment customarily employed for acontinuous process. The water of the reaction is optionally removed fromthe reaction mass with the aid of an inert gas purge.

[0013] The temperature of the process is controlled in order to obtain ahigh yield of 3-methyl-tetrahydrofuran. The temperature of the reactioncan range of from about 100° C. to about 250° C. A temperature of fromabout 200° C. to about 250° C. is preferred. A more preferredtemperature is from about 215° C. to about 240° C. A pressure of fromabout 1 MPa to about 15 MPa is employed in the reaction. A pressure offrom about 8 MPa to about 10 MPa is preferred.

[0014] By “acid promoter” is meant a compound acidic in nature that isadded to enhance the physical or chemical function of a catalyst.

[0015] By “metal promoter” is meant a metallic compound that is added toenhance the physical or chemical function of a catalyst.

[0016] A catalyst is a substance that affects the rate of the reactionbut not the reaction equilibrium, and emerges from the process,chemically unchanged. A chemical promoter generally augments theactivity of a catalyst. The promoter may be incorporated into thecatalyst during any step in the chemical processing of the catalystconstituent. The chemical promoter generally enhances physical orchemical function of the catalyst agent, but it can also be added toretard undesirable side reactions.

[0017] Reduction of 2-methyl-gamma butyrolactone to3-methyl-tetrahydrofuran product and water is effected in presence of ametal catalyst. The catalytic metal component of the catalyst isselected from the group consisting of metals of Group 7, 8, 9, and 10,of the Periodic Table, compounds of a metal of group 7, 8, 9, and 10 ofthe Periodic Table, compounds thereof, combinations thereof, copper, andcopper compounds.

[0018] The catalytic metal used in the process disclosed here may beused as a supported or as an unsupported catalyst. A supported catalystis one in which the active catalyst agent is deposited on a supportmaterial by spraying, soaking or physical mixing, followed by drying,calcination, and if necessary, activation through methods such asreduction or oxidation. Materials frequently used as support are poroussolids with high total surface areas (external and internal) which canprovide high concentrations of active sites per unit weight of catalyst.The catalyst support may enhance the function of the catalyst agent. Acatalyst which is not supported on a catalyst support material is anunsupported catalyst.

[0019] A support material is selected from the group consisting ofcarbon, alumina, silica, silica-alumina, titania, and a combinationthereof. Moreover, supported catalytic metal/s may have the samesupporting material or different supporting material. A more preferredsupport is carbon. The carbon can be a commercially available carbonsuch as Calsicat C, Sibunit C, or Calgon C (sold under the tradenameCentaur(R)).

[0020] A preferred catalytic metal content range in a supported catalystis from about 0.1% to about 25%. One preferred catalytic metal contentis from about 1% to about 7%, and a further preferred catalytic metalcontent is from about 1% to about 5%. Another preferred catalytic metalcontent is from about 18% to about 22%.

[0021] Preferred combinations of catalytic metal and support systemincludes rhodium on carbon, rhenium on carbon, rhenium on alumina,iridium on carbon, iridium on alumina, ruthenium on alumina, and acombination of (ruthenium and rhenium) on carbon.

[0022] An acid promoter may be used in the process of the presentinvention. Suitable promoters include, those acids with a pKa less thanabout 4, preferably with a pKa less than about 2, including inorganicacids, organic sulfonic acids, heteropolyacids, perfluoroalkyl-sulfonicacids, and mixtures thereof. Also suitable are metal salts of acids withpKa less than about 4, including metal sulfonates, metaltrifluoroacetates, metal triflates, and mixtures thereof includingmixtures of salts with their conjugate acids. Specific examples ofpromoters include sulfuric acid, fluorosulfonic acid, phosphoric acid,p-toluenesulfonic acid, benzenesulfonic acid, phosphotungtstic acid,phosphomolybdic acid, trifluromethanesulfonic acid,1,1,2,2-tetrafluroethanesulfonic acid, 1,2,3,2,3,3-hexapropanesulfonicacid, bismuth triflate, yttrium triflate, ytterbium triflate, neodymiumtriflate, lanthanum triflate, scandium triflate, and zirconium triflate.A preferred promoter is selected from group consisting of Zn(BF4)₂,zeolite CBV-1502, zeolite 20A, zeolite CBV 3020E, 13% Nafion(R) andmethane sulfonic acid. The acid promoter is used in concentration offrom 0.1% to 5% by weight of the reactant. A preferred concentration ofthe promoter is in the range of 0.25% to 2.5% by weight of the reactant.

[0023] Suitable heterogeneous acid promoters are zeolites, fluorinatedalumina, acid-treated silica, acid treated silica-alumina, acid treatedclays, heterogeneous heteropolyacids and sulfated zirconia.Heterogeneous acid promoters are preferred due to ease of separation,but both heterogeneous and homogeneous acid promoters may be used.

[0024] A metal promoter may be used optionally with the acid promoter inthe process of the present invention. Suitable metal promoters includetin, zinc, copper, gold, silver, and combinations thereof. The preferredmetal promoter is tin.

Experimental

[0025] The following abbreviations are used in the Examples: ESCATSeries of catalysts provided by Engelhard Corp. Calsicat Carbon Catalystsupport from Engelhard Corp. Sibunit Carbon Catalyst support from Inst.of Technical Carbon, Omsk, Russia JM-A11108 Carbon Catalyst support fromJohnson Matthey, Inc. Calgon Carbon Catalyst support from Calgon Corp.under the brand name of Centaur(R) CBV-3020E Type of Zeolite acidpromoter 20-A Type of Zeolite acid promoter CBV-1502 Type of Zeoliteacid promoter

[0026] A commercially available support such as carbon, alumina, silica,silica-alumina, titania available from Engelhard Corp. (E. Windsor,Conn.) was impregnated by incipient wetness with a metal salt. Theprecursors used were NiCl₂.6H₂O (Alfa Chemical Co.), Re₂O₇ (AlfaChemical Co.), PdCl₂ (Alfa Chemical Co.), RuCl₃.xH₂O (Aldrich ChemicalCo.). H₂PtCl₆ (Johnson Matthey, Inc., W. Deptford, N.J.), CrCl₃.6H₂O(Mallinckrodt Baker, Inc.), 5% Rh using RhCl₃.xH₂O (Alfa Chemical Co.).The samples were dried and reduced at 300-450° C. in H₂ for 2 hours.

[0027] The carbon used was commercially available as Calsicat Carbon,Sibunit Carbon, or Calgon Carbon (Centaur(R)). Calsicat Carbon is lot.no. S-96-140 from Engelhard Corp, Beachwood, Ohio. Sibunit Carbon isSibunit-2 from Institute of Technical Carbon, 5th Kordnaya, Omsk 64418,Russia. Calgon Carbon is PCB Carbon from Calgon Corp.(under theregistered trademark of Centaur(R)).

EXAMPLE-1 Catalyst Preparation 5%Pt on Acid Washed Calsicat Carbon

[0028] In a 150 ml beaker, a solution was made up of 4.5 ml, 0.3 MH₂PtCl₆ with 4.0 ml deionized H₂O. To the beaker were added 4.75 gCalsicat Acid Washed Carbon (12×20 mesh, dried at 120° C. overnight).The slurry was allowed to stand at room temperature for 1 hr withoccasional stirring and then dried at 120° C. overnight with frequentstirring (until free flowing).

[0029] In an alumina boat, in a quartz lined tube furnace, the catalystwas purged with 500 SCCM N₂ at room temperature for 15 min and then with100 SCCM He at room temperature for 15 min. The catalyst was heated to150° C. and held at 150° C. under He for 1 hr. At this point, 100 SCCMH₂ were added and the sample was held at 150° C. under He and H₂ for 1hr. The temperature was increased to 300° C. and the catalyst wasreduced at 300° C. under He-H₂ for 8 hrs. The H₂ was stopped, the samplewas held at 300° C. under He for 30 min and then cooled to roomtemperature in flowing He. The catalyst was finally passivated in 1.5%O₂ in N₂ at 500 SCCM for 1 hour at room temperature and weighed 4.93grams when unloaded.

EXAMPLES 1-64 Reduction of 2-methyl-gamma-butyrolactone to3-methyl-tetrahydrofuran

[0030] 50% 2-methyl-gamma-butyrolactone in dioxane (970.0 mg, 4.84mmole) and an amount of catalyst and support as indicated in Table 1,were added to a 2 ml reactor. The reactor was sealed and charged with6.89 MPa of H₂, and heated to 225° C. then cooled rapidly. The reactionwas stopped after 4 hours. An internal standard (2-methoxy ethyl ether)was added to the reaction mixture and GC analysis was performed on aHP-6890 GC with a Chrompack column (CP-WAX 58, 25 M×0.25 MM). An acidpromoter was not used for examples 1-33. An acid promoter was used forexamples 34-66. TABLE 1 H₂ 2-Me-GBL 3-methyl- Ex. Time Temp. PressureCatalyst/ Conversion tetrahydrofuran No. (hrs) (° C.) (MPa) Support Acid(%) Selectivity (%) 1. 4 225 6.89 1% Ru/6% Re/C 19.56 49.12 2. 4 2256.89 5% Rh/Sibunit C 9.21 12.76 3. 4 225 6.89 5% Pt/Sibunit C 2.12 29.234. 4 225 6.89 5% Ru/Calsicat C 9.87 77.56 5. 4 225 6.89 5% Rh/Calsicat C5.12 91.38 6. 4 225 6.89 5% Pd/Calsicat C 2.44 70.21 7. 4 225 6.89 5%Re/Calsicat C 31.24 97.91 8. 4 225 6.89 5% Ir/Calsicat C 8.95 92.01 9. 4225 6.89 5% Pt/Sibunit C 2.40 82.19 10. 4 225 6.89 5% Ru/Al₂O₃ 1.6095.57 11. 4 225 6.89 5% Rh/Al₂O₃ 26.60 3.45 12. 4 225 6.89 5% Pd/Al₂O₃88.01 0.80 13. 4 225 6.89 5% Re/Al₂O₃ 7.33 97.75 14. 4 225 6.89 5%Ir/Al₂O₃ 2.00 96.21 15. 4 225 6.89 5% Pt/Al₂O₃ 10.62 24.69 16. 4 2256.89 5% Ru/SiO₂ 5.50 10.01 17. 4 225 6.89 5% Rh/SiO₂ 19.51 1.67 18. 4225 6.89 5% Pd/SiO₂ 31.30 1.23 19. 4 225 6.89 5% Re/SiO₂ 8.46 41.56 20.4 225 6.89 5% Ir/SiO₂ 1.83 31.17 21. 4 225 6.89 5% Pt/SiO₂ 17.41 3.5022. 4 225 6.89 5% Re/Sibunit C 32.87 53.09 23. 4 225 6.89 5% Re/Calgon C14.50 31.75 24. 4 225 6.89 5% Re/Sibunit 42.45 31.39 C(400C) 25. 4 2256.89 5% Re/Sibunit 24.33 46.33 C(450C) 26. 4 225 6.89 10% Re/Sibunit36.34 35.26 C(400C) 27. 4 225 6.89 10% Re/Sibunit 44.95 30.02 C(450C)28. 4 225 6.89 5% Re/Calsicat 36.24 94.20 C(400C) 29. 4 225 6.89 5%Re/Calsicat 35.77 91.63 C(450C) 30. 4 225 6.89 10% Re/Calsicat 46.1390.11 C(400C) 31. 4 225 6.89 10% Re/Calsicat 49.41 91.19 C(450C) 32. 4225 6.89 20% Re/Calsicat 64.74 86.26 C(400C) 33. 4 225 6.89 20%Re/Calsicat 72.11 78.25 C(450C) 34. 4 225 6.89 1% Ru/6% Re/C Zn(BF4)218.68 80.61 35. 4 225 6.89 1% Ru/6% Re/C CBV-1502 10.94 89.96 36. 4 2256.89 1% Ru/6% Re/C 20A 2.70 48.33 37. 4 225 6.89 5% Rh/Sibunit CZn(BF4)2 6.15 6.79 38. 4 225 6.89 5% Rh/Sibunit C CBV-1502 2.21 40.4839. 4 225 6.89 5% Pt/Sibunit C Zn(BF4)2 1.37 31.66 40. 4 225 6.89 5%Pt/Sibunit C CBV-1502 4.83 6.35 41. 4 225 6.89 5% Pd/Calsicat C Zn(BF4)210.08 92.06 42. 4 225 6.89 5% Pd/Calsicat C CBV- 4.75 8.31 3020E 43. 4225 6.89 5% Pd/Calsicat C 13% NAFI 1.37 18.57 ON 44. 4 225 6.89 5%Pd/Calsicat C MSA 2.48 11.71 45. 4 225 6.89 5% Ru/Calsicat C Zn(BF4)26.90 86.35 46. 4 225 6.89 5% Ru/Calsicat C CBV- 3.16 62.88 3020E 47. 4225 6.89 5% Ru/Calsicat C 13% NAFI 6.11 57.65 ON 48. 4 225 6.89 5%Ru/Calsicat C MSA 8.59 32.53 49. 4 225 6.89 5% Re/Calsicat C Zn(BF4)24.07 72.97 50. 4 225 6.89 5% Re/Calsicat C CBV- 8.42 79.78 3020E 51. 4225 6.89 5% Re/Calsicat C 13% NAFI 10.21 91.35 ON 52. 4 225 6.89 5%Re/Calsicat C MSA 16.03 92.79 53. 4 225 6.89 5% Rh/Calsicat C Zn(BF4)20.69 57.72 54. 4 225 6.89 5% Rh/Calsicat C CBV- 1.01 70.50 3020E 55. 4225 6.89 5% Rh/Calsicat C 13% NAFI 1.14 42.94 ON(R) 56. 4 225 6.89 5%Rh/Calsicat C MSA 2.34 38.14 57. 4 225 6.89 5% Pt/Sibunit C Zn(BF4)22.01 35.66 58. 4 225 6.89 5% Pt/Sibunit C CBV- 0.61 31.75 3020E 59. 4225 6.89 5% Pt/Sibunit C 13% NAFI 2.07 30.65 ON 60. 4 225 6.89 5%Pt/Sibunit C MSA 2.67 24.09 61. 4 225 6.89 5% Ir/Calsicat C Zn(BF4)21.39 71.80 62. 4 225 6.89 5% Ir/Calsicat C CBV- 2.63 54.40 3020E 63. 4225 6.89 5% Ir/Calsicat C 13% NAFI 1.77 63.55 ON(R) 64. 4 225 6.89 5%Ir/Calsicat C MSA 3.03 55.50

What is claimed is:
 1. A process for preparing 3-methyl-tetrahydrofurancomprising heating 2-methyl-γ-butytrolactone represented by formula (I)in the presence of hydrogen and a catalytic amount of a metal catalyst.


2. The process as recited in claim 1, wherein the metal catalyst isselected from the group consisting of metals of Group 7, 8, 9, and 10,of the Periodic Table, compounds of a metal of group 7, 8, 9, and 10 ofthe Periodic Table, compounds thereof, combinations thereof, copper, andcopper compounds.
 3. The process as recited in claim 1, wherein themetal catalyst is supported on a catalyst support.
 4. The process asrecited in claim 3, wherein the catalyst support is selected from thegroup consisting of carbon, alumina, silica, zirconia, silica-alumina,titania, compounds thereof and combinations thereof.
 5. The process asrecited in claim 1, wherein the metal catalyst is promoted with at leastone promoter.
 6. The process as recited in claim 5, wherein the promoteris a metal.
 7. The process as recited in claim 5, wherein the metalpromoter is selected from the group consisting of tin, zinc, copper,gold, silver, and combinations thereof.
 8. The process as recited inclaim 5, wherein the promoter is an acid.
 9. The process as recited inclaim 8, wherein the acid promoter is an acid with a pKa less than about4, or a metal salt thereof.
 10. The process as recited in claim 8,wherein the acid promoter is selected from the group consisting ofinorganic acids, organic sulfonic acids, heteropolyacids, perfluoroalkylsulfonic acids, and metal salts thereof.
 11. The process as recited inclaim 10, wherein the acid promoter is selected from the groupconsisting of sulfuric acid, fluorosulfonic acid, phosphoric acid,p-toluenesulfonic acid, benzenesulfonic acid, phosphotungtstic acid,phosphomolybdic acid, trifluromethanesulfonic acid,1,1,2,2-tetrafluorethanesulfonic acid,1,1,1,2,3,4-hexafluorpropanesulfonic acid, bismuth triflate, yttriumtriflate, ytterbium triflate, neodymium triflate, lanthanum triflate,scandium triflate, and zirconium triflate.
 12. The process as recited inclaim 8, wherein the acid promoter is selected from the group consistingof zeolites, fluorinated alumina, sulfuric acid-treated silica, sulfuricacid-treated silica-alumina, heteropolyacids supported on zirconia,titania, alumina, and/or silica.
 13. The process as recited in claim 11,wherein the acid promoter is Zn(BF₄)₂.
 15. The process as recited inclaim 11, wherein the acid promoter is zeolite CBV-1502.
 16. The processas recited in claim 11, wherein the acid promoter is zeolite CBV-20A.17. The process as recited in claim 11, wherein the acid promoter iszeolite 3020E.
 18. The process as recited in claim 11, wherein the acidpromoter is methane sulfonic acid.
 19. The process as recited in claim8, wherein the acid promoter is Nafion(R).
 20. A process for preparing3-methyl-tetrahydrofuran comprising the step of heating2-methyl-gamma-butytrolactone represented by formula (I) in the presenceof hydrogen, a catalytic amount of a metal catalyst, an acid promoterand a metal promoter.


21. The process as recited in claim 1, wherein said process is performedat a temperature from about 100° C. to about 250° C.
 22. The process asrecited in claim 21, wherein said process is performed at a temperaturefrom about 200° C. to about 250° C.
 23. The process as recited in claim22, wherein said process is performed at a temperature from about 215°C. to about 240° C.
 24. The process as recited in claim 1, wherein theprocess is performed at a pressure from about 1.0 MPa to about 15.0 MPa.25. The process as recited in claim 24, wherein the process is performedat a pressure from about 8.0 MPa to about 10.0 MPa.
 26. The process asrecited in claim 1, wherein the process is performed at a temperaturefrom about 215° C. to about 250° C. and a pressure from about 8.0 MPa toabout 10.0 MPa.
 27. The process as recited in claim 3, wherein the metalcatalyst is rhenium and the catalyst support is carbon.
 28. The processas recited in claim 27, wherein the process is performed at atemperature from about 215° C. to about 250° C. and a pressure fromabout 8.0 MPa to about 10.0 MPa.
 29. The process as recited in claim 27,wherein the metal catalyst is present in an amount from 0.1% to 5.0%.30. The process as recited in claim 27, wherein the metal catalyst ispresent in an amount from 5.0% to 10.0%.
 31. The process as recited inclaim 27, wherein the metal catalyst is present in an amount from 10.0to 20.0%.
 32. The process as recited in claim 1, wherein the metalcatalyst is copper chromite.